A wall defect is generally a hole in the wall of the tissue of an animal, such as humans, or a hole in the wall of a container, tank, bag filter, or planar filter, tent, inflatable device, etc. In muscles or tissues of animals, repairs have been accomplished by inserting an occlusion or septal closure device into the aperture or defect. Such devices include those taught by U.S. Pat. Nos. 5,334,217 to Das and 5,108,420 to Marks.
The Das patent describes a septal defect closure device, its use and method of assembly, where individual disks of a thin flexible material are supported by a super-elastic material and are used to occlude a wall defect. The disks are conjointly attached to one another at the center of the disk. The thin flexible material used in the Das patent can include nylon, polyester, polypropylene and polytetrafluoroethylene (PTFE) polymers. The super-elastic material is a NiTi alloy (or "nitinol".)
The super-elastic material of the Das patent is formed into a frame having several legs and can assume geometrical configurations such as triangles, hexagons, circles, and stars. A membrane is wrapped around the legs of the frame. The loops between adjacent legs bias the legs outwardly, to form a concave membrane surface, which is maintained in a highly tensioned fashion.
The Marks patent describes an occlusion device that can be transported via a catheter in a compressed state. Once through an aperture to be occluded, the device is released and wires supporting two membranes are positioned on each side of the aperture. A domed or umbrella shaped configuration is formed and the support wires urge the membranes towards one another and the wall where the aperture is located.
These prior devices have numerous drawbacks. The support frames of the Das patent include resilient wire loops where leg ends of the frame meet and are attached to one another. The loops generally extend beyond the periphery of the membrane and can irritate or damage adjacent muscle or tissue.
Similarly, the exposed wires of the Marks device act as an irritant to tissue or muscle adjacent the aperture or septum. Here the bare sharp ends of the wire structure can further cause tissue erosion.
The Das and Marks patent devices use a membrane of conventional thickness that when folded over a wire add undesired thickness to the device. Additionally, the patents rely on peripheral membrane support which leaves the central occlusion covering portion of the membrane vulnerable.
In the Das patent design, each leg is provided with a bend at the middle of its length. This bend may tend to fold the device when the frame is sitting against a very flexible tissue and the membrane is pressurized by the blood. This may be the potential mechanism of failure as reported in Agarwal, S. K., Ghosh, P. K. and Mittal, P. K., "Failure of Devices Used for Closure of Atrial Septal Defects: Mechanisms and Management," The Journal of Thoracic and Cardiovascular Surgery, Vol. 112, No. 1, 1996.
Finally, it is believed that none of the previously available devices have provided a sufficiently small enough insertion diameter and/or collapsed flexibility. This limitation has restricted the utility and ease of use of such devices.
Thus, in view of the above, it is desirable to provide a closure device that eliminates or significantly minimizes the traumatizing effect of existing closure devices. Further, it is desirable to provide such a device to be stable under physiological loading conditions when situated against the anatomical tissue structure. It is additionally desirable to provide a defect closure device that is collapsible or compressible so that it may fit into a 9F (9 French), preferably 5F or 4F or smaller catheter for deployment in a defect.
These drawbacks and disadvantages of the prior devices have been addressed and overcome by the inventions described in the two co-pending patent applications. These prior inventive devices employ unique nitinol frames combined with thin expanded PTFE membranes to create defect closure devices that function better than any previous defect closure devices. Of particular benefit of these devices is the fact that they are capable of being compacted into very small delivery tools and then deploy to fully operational diameters. Additionally, unlike some previous defect closure devices, these inventive devices provide excellent protection of tissue from damage by the frame, which is protected under the expanded PTFE cover. Further, these inventive devices also are capable of being relatively easily withdrawn remotely from the defect site in the case they need to be retrieved.
Despite the excellent properties of the defect closure devices disclosed in the parent applications, on-going development work has revealed that further improvements may be possible on these devices. First, it has been discovered that with devices with helical frames the device must be carefully deployed to assure that the helical frame initially starts to expand with the correct spiral. If the helix starts unwrapping in the wrong direction, the operator must withdraw the device back into the delivery tool and attempt deployment a second time to assure that the device expands correctly. Accordingly, a frame which consistently deploys with the correct bias in the helical frame is believed desirable.
Second, the use of the parent devices within tortuous anatomy generally requires the use of separate guidewire catheters or similar devices to help negotiate the device delivery apparatus to the deployment site. This requires both the use of additional equipment and often taxes space limitations at a surgical site. Thus, it is further believed desirable to incorporate a simpler and more compact system that can assist in negotiating the deployment apparatus to the defect site.